The invention relates to devices for removing water vapor from air, and more particularly to electrostatic devices for removing droplets from gaseous mediums without expenditure of large amounts of energy.
The requirement for removal of water vapor from air to improve comfort is well-known. One known method of removing water vapor to reduce the relative humidity of air is to pass the humid air through absorbent or hydroscopic drying material that eventually becomes saturated. The saturated drying material must be discarded or recycled by heating, using a significant amount of energy, before reuse. Other techniques for removal of water vapor or other vapor from air, such as removal of organic vapors from dry cleaning and painting operations, involve the use of activated charcoal or zeolite absorbents that have limited capacity and must be recycled by heating. Passing moist air through refrigerated coils to condense the vapor from the air is another known technique for reducing the relative humidity of air. This technique requires a large amount of energy to compress the refrigerant gas and then pass it through cooling coils to induce condensation of high pressure refrigerant gas to its liquid state. The condensed liquid then is allowed to expand back into the gas phase thereby taking heat from air that is to be cooled to the dew point to induce condensation of water.
All of the above processes require substantial amounts of energy and contribute to the cost of dehumidifying air. As will be explained, an advantage of the present invention is that the air need not be cooled in order to remove the moisture therefrom.
Electrostatic precipitators commonly have been used to remove particles from an air stream or gas stream in many industrial discharge processes to prevent contamination of the atmosphere. Electrostatic precipitators typically include corona discharge arrays that include a large array of closely spaced, conductive pointed needles and a conductive collector to produce strong electrostatic field gradients. The high electric fields ionize or charge minute particles in air or gas passing through the systems. The ionized particles then migrate and adhere to the conductive collector.
The collected particles may be removed by shaking the collector or spraying it with water. If high resistivity particles (e.g., Western fly ash) are to be collected, water may be sprayed into the system during the charging/collection operation to induce particle agglomeration and reduce the electrical resistance of the collected dust. The state-of-the-art is generally indicated in U.S. Pat. Nos. 4,264,343, 4,194,888, 4,094,653, 4,072,477, 3,890,103, 3,826,063, 3,124,437, 1,393,712 and 1,130,212 and French Patent No. 2.229.468.
U.S. Pat. No. 3,750,373 by Olson discloses a structure for removing mist from a gas stream, in which moisture laden gas passes through tubes containing a helical wrap of Starr type wire having a plurality of outwardly directed points thereon and disposed within conductive tubes. An electric field applied between the housing and the wire causes minute droplets constituting the mist to form larger droplets that fall to the bottom of the housing and are collected and drained away.
In the system of U.S. Pat. No. 3,750,373, the "mist" consists of small droplets of liquid water. These "mist" droplets can be induced to agglomerate into large drops quite easily and are thereby removed from the airstream.
There is believed to be a wide variety of uses for a low cost, low energy consumption device for removing mist, and from air and gases. Up to now, however, no commercially viable technique other than use of the above-mentioned absorbent materials or refrigerated coils to promote condensation has been demonstrated.